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Re: L1 orbit maybe interresting for HAM ?



William Leijenaar, PE1RAH, wrote:

>I just read about the ACE satellite which has a very special orbit.
>Its orbit is called L1, what is between the sun and earth gravity.
>The satellite stays at a fixed distance to the earth, while orbiting the sun


>I think this kind of orbit would be interresting for far distance 
>communication :-) Not that far as P5A to Mars, but not that short as P3d.

>The only problem is maybe radiation, heat, and sun noise :-(
>Its just an idea...


This is roughly the same discussion we have here every so often about putting
a ham repeater on the moon. The L1 Lagrange point is roughly four times
farther out than the moon, thus the signal strength would be 1/16 of that from
a similar transmitter placed on the moon. For a transponder, you would suffer
the 16 times loss both going up and coming down. Only a very few Moonbounce
class amateurs would be able to make any use of it at all. The average ham
will have no hope of working such a satellite.

The best orbits for ham satellites are indeed circular or elliptical orbits as
far out as geosynchronous altitude. Once you get far enough away from the
Earth to see an entire hemisphere at once, there is nothing to be gained by
going farther out, and a tremendous cost to be paid in extra path loss. 

Domenico, i8CVS, wrote:

>Put by hand the following keplerian elements in your tracking program 
>and see what happen in a "Apogee at Constant time-of-day Equatorial" or
>ACE orbit.

>You will be very surprised about the performance of a ACE orbit

Sorry Domenico, but you are confusing the "Apogee at Constant time-of-day
Equatorial" (ACE) orbit with the "Advanced Composition Explorer" (ACE)
spacecraft. Two entirely different animals. 

The ACE project homepage is http://www.srl.caltech.edu/ACE/

A tutorial on the Lagrange points (including a link to a mathematical
derivation) can be found at: 
http://www.physics.montana.edu/faculty/cornish/lagrange.html

The L1 point is an unstable equilibrium point, in the same sense that a marble
balanced on top of a beach ball is in equilibrium. The slightest disturbance
will cause it to fall off. The three satellites stationed at the Earth-Sun L1
point (SOHO, ACE and WIND) all use regular bursts from station keeping
thrusters to correct their position. When they eventually run out of fuel they
will depart from the L1 point and drift off into solar orbit. 

Finally, Phil Karn's work in designing a low cost ground station for ACE solar
wind data is at http://www.ka9q.net/code/acedemod/

Dan Schultz N8FGV


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